AQP4 and neuromyelitis optica: NMO CSF-derived rAbs specific for AQP4 failed to recognize denatured AQP4 protein monomers in SDS-PAGE protein immunoblots of lysates from AQP4-transfected CHOK1 cells (Fig. 2), indicating that CSF-derived Abs likely recognize conformational epitopes formed by the assembly of AQP4 tetramers and OAPs at the cell surface.